The mechanics of bronchoconstriction cause airway epithelial damage and inflammation by excess crowding-induced extrusion.

Asthma is a common disease characterized by airway constriction, excess mucus, and inflammation. Although asthma is an inflammatory disease, subclassed by different endotypes, triggers, and immune responses, the defining diagnostic symptom is mechanical bronchoconstriction from uncontrolled smooth muscle contraction. We previously discovered a conserved process that drives epithelial cell death in response to mechanical cell crowding called epithelial cell extrusion 1, 2 . Because modest crowding triggers extrusion to maintain constant homeostatic epithelial cell densities, we reasoned that the pathological crowding from bronchoconstriction might potentially destroy the airway epithelial barrier, causing the typical inflammatory period that follows an asthma attack. Here, using immune-primed mice, we show that the crowding of bronchoconstriction causes excess epithelial cell extrusion and damage, resulting in inflammation in distal airways, and mucus secretion in proximal airways. Surprisingly, relaxing airways following bronchoconstriction with the current rescue treatment, albuterol, did not prevent epithelial extrusion and destruction, inflammation, or mucus secretion. However, inhibiting canonical live cell extrusion signaling during bronchoconstriction with stretch-activated/TRP channel or sphingosine 1-phosphate (S1P) inhibitors blocked all downstream symptoms. Our findings propose a new etiology for asthma where the extreme mechanical crowding from a broncho constrictive attack causes inflammation by wounding airway epithelium. Whereas most therapies focus on modulating down-stream inflammatory symptoms, our studies suggest that blocking epithelial extrusion could prevent the feed-forward asthma inflammatory cycle.